Currently, there exist specialist machines (“telecine” machines) to scan cinema style motion picture film, and derive electrical signals for recording onto video tape or broadcasting as television pictures. One example of this is the ‘URSA’RTM telecine manufactured by Cintel International Limited in Ware, England. Machines for scanning film at resolutions higher than those required for television and/or in non-real time are also known.
It is known to provide appearance attribute correction means in these telecines such that scenes may be studied, and an appearance attribute correction data set may be determined for individual scenes. The appearance attributes to be corrected could for example be chrominance, luminance or saturation of an image or they could be attributes relating to other characteristics of the image such as for example, sharpness or texture. The process of building up a series of appearance attribute correction values for a number of scenes, which is then used in a real time ‘transfer’ mode to effect the appearance attribute correction is taught in U.S. Pat. No. 4,096,523. An example of a telecine controller and programmer embodying such a process is the ‘POGLE’ produced by Pandora International Limited. In such a system, the appearance attribute correction data set is obtained by an operator viewing a scanned image on a monitor screen and manually adjusting the colour of the image until he is happy with the result. The manual adjustments made by the controller are then stored so that they can be applied as the image is rescanned as described above.
It is also known to provide a digital video processor downstream of the telecine machine which can carry out more detailed colour corrections at the request of a user than would be possible within the telecine machine. Examples of digital video processors are the DCP manufactured by Pandora International Limited (described in UK patent application No. GB 2278514A) and the ‘Megadef’, also manufactured by Pandora International Limited.
In the past, telecine machines were used to produce video images for television at standard definition with an aspect ratio of 4:3. However, television images are now produced at either standard definition or high definition and the aspect ratio can be either 4:3, 14:9 or 16:9. In addition, telecine machines and film scanners are being used increasingly to scan film at much higher resolutions than is required for television, such as at a resolution of 2000 lines by 3000 pixels or higher (“film resolution”).
Consequently, there is a need to provide a system for processing digital images obtained from scanning cinematographic film which provides good accuracy independent of the resolution at which the film has been scanned.
In prior art systems, digital images obtained by a telecine machine would be viewed in the editing suite by a first operator. This would usually be somebody relatively junior and he would apply a first set of colour or appearance attribute corrections to the images obtained and the amended images would then be stored. Subsequently, further fine tuning to the colour corrections would be carried out (usually by a more senior operator). To do this, the operator would retrieve and view the stored corrected image and would apply further colour corrections to that corrected image.
Each set of corrections applied to the image are usually implemented by processing through one or more look-up tables containing the required corrections. The problem with this is that the look-up tables crush the data passing through them unless no change is made to the data. Thus, each time that a new set of corrections are applied to the image and the corrected image is subsequently stored, some more data will be lost. As many different sets of corrections will often be made to an image before it is ready to be broadcast or recorded onto video tape for public viewing, the final quality of the image obtained may be substantially worse than that originally produced by the telecine.